What is the electron output constancy requirement?

• A. 3% (weekly, except machines requiring daily e-monitoring)
• B. 3% (daily)
• C. 5% (weekly)
• D. 2% (weekly)

Answer: (A)

Output constancy for electron beams is about how much the delivered dose can drift from the reference value while still being acceptable. The standard tolerance is 3%, meaning the measured output should stay within ±3% of the reference. The usual practice is to perform these checks weekly. However, if a machine has daily electronic monitoring (daily e-monitoring) in place, the constancy checks are done daily. That combination—3% tolerance with weekly checks, except for machines that require daily e-monitoring—matches the given correct option. The other options mix different percentages or call for daily checks across the board, which isn’t aligned with typical practice.